IgA class autoantibodies to beta 2-glycoprotein I (β2-GPI) have recently been reported in patients with acute myocardial infarction and also in patients with ischemic stroke (Ranzolin A, et al., Arg Bras Cardiol. 83(2):141-4; 137-40 (2004); Kahles T, et al., Rheumatology 44(9):1161-5 (2005); Staub H L, et al., Arg Neuropsiquiat 61(3B):757-63 (2003)). A striking observation from two of these studies was that the IgA β2-GPI autoantibodies were usually detected in patients that were negative for IgA anti-cardiolipin antibodies (ACA) (Ranzolin A, et al., Arg Bras Cardiol. 83(2):141-4; 137-40 (2004); Staub H L, Arg Neuropsiquiat 61(3B):757-63 (2003)). This finding is in sharp contrast to that observed in patients with anti-phospholipid syndrome (APS), where both anti-β2-GPI and anti-cardiolipin antibodies are usually positive.
β2-GPI is a serum protein composed of five homologous domains numbered 1-5 from the N terminus. Domains 1-4 are composed of ˜60 amino acids that contain a motif characterized by a framework of four conserved cysteine residues, which form two internal disulfide bridges (Lozier, J. et al., PNAS 81:3640-3644 (1984)). The fifth domain differs from domains 1-4 in that it contains 82 amino acid residues with six cysteines. The fifth domain contains the phospholipid binding site (Hunt, J., et al., PNAS 90:2141-2145 (1993)).
Conflicting findings have been published concerning the domain specificity of anti-β2-GPI autoantibodies. For example, in one study, it was shown that using recombinant β2-GPI and β2-GPI domain-deleted mutants (Dms) expressed in insect cells, that anti-β2-GPI autoantibodies found in serum samples from patients with APS recognize domain 1 of β2-GPI (Iverson, G M, et al., PNAS 95:15542-15546 (1998).
There are also reports that IgG anti-β2-GPI autoantibodies in patients with APS recognize epitopes on domains 3, 4 and 5 of β2-GPI (Blank, M, et al., PNAS 96:5164-8 (1999); Blank, M, et al., PNAS 96:5164-8 (1999); Koike T, et al., J. Autoimmun 15: 97-100 (2000); Yang C D, et al., APLAR J Rheumatol 1:96-100 (1997); Iverson, G M, et al., J. of Autoimmunity 18:289-297 (2002); and McNeeley P A, et al., Thromb Haemost 86:590-5 (2001)).
Accordingly, there is a need for an enhanced understanding of the antibody profiles exhibited by APS patents (cardiolipin IgG positive/β2-GPI IgG/IgA positive), and the differences between these profiles and the profiles exhibited by cardiovascular patients with acute ischemic disease (cardiolipin IgG/IgA negative/β2-GPI IgA positive), which is based on differing domain-specificity of the APS and cardiovascular patient's antibodies. The present invention provides such an enhanced understanding, and relates to the finding that IgA anti-β2-GPI autoantibodies that bind to domain 4 are found in a high percentage of patients with APS and various cardiovascular diseases.